| MR Elastography |
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Thursday 23 April 2009 |
| Room 315 |
16:00-18:00 |
Moderators: |
Richard L. Ehman and Donald B. Plewes |
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16:00 |
709. |
Validity of a 2-D Wave Field
Model in MR Elastography of the Liver |
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Meng Yin1,
Kevin J. Glaser1, Jayant A. Talwalkar2,
Armando Manduca1, Richard L. Ehman1
1Department of Radiology, Mayo Clinic,
Rochester, MN, USA; 2Division of
Gastroenterology & Hepatology, Mayo Clinic,
Rochester, MN, USA |
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One advantage of liver
MRE over biopsy or ultrasound-based transient
elastography is its ability to reduce sampling error
by measuring liver stiffness in multiple areas of
the liver. While full 7-D wave imaging offers valid
measurement of stiffness throughout the liver, the
2-D approach may also provide valid results in a
significant part of the volume, with a substantially
reduced imaging time. This investigation compared
these two approaches, validated the key element of
the protocol that makes this possible – the
optimized acoustic driver system can provide a wave
propagation geometry that is suitable for reliable
2-D wave imaging. |
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16:12 |
710. |
Vitreal Viscoelasticity
Revealed by Motion-Encoded MRI |
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Marco Piccirelli1,2,
Oliver Bergamin2, Klara Landau2,
Peter Boesiger1, Roger Luechinger1
1Institute for Biomedical Engineering,
University and ETH Zurich, Zurich, Switzerland;
2Department of Ophthalmology, University
Hospital, Zurich, Switzerland |
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The vitreous shear
stress can damage the retina and induce visual loss.
Up to now, the vitreous viscoelasticity has only
been measured ex-vivo. However, the
intravitreal membranes may impact on the shear
stress. We determined the vitreous deformation
properties in-vivo with intact intravitreal
membranes, using peak-combination HARP on CSPAMM
images. The vitreous viscoelasticity was determined
by fitting the deformation with an analytic model.
We were able to split the subjects into 4 groups:
gel-like, intermediate, liquefied, and polyphasic
vitreous. Our results contrasted with ex-vivo
data, which do not include the intravitreal
membranes. |
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16:24 |
711. |
Application of DENSE
MR-Elastography to the Human Heart: First in Vivo
Results |
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Benjamin Robert1,
Ralph Sinkus1, Jean-Luc Gennisson1,
Mathias Fink1
1Laboratoire Ondes et Acoustique, Ecole
Supérieure de Physique et Chimie Industrielles,
Paris, France |
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Cardiac MR-Elastography
presents several challenges due to short T2* and
periodic myocardium activity. Moreover, low
frequency elastic waves should be used as the heart
is located deeply within the chest. Thus,
conventional MRE has failed to be implemented to
myocardium. A new MRE sequence has been derived from
DENSE sequence, and it is applied to two healthy
volunteers. In vivo cardiac feasibility is
shown, and elastograms are estimated for four
different heart phases during diastole for both
volunteers. The shear modulus maps are characterized
by an increase during diastole as the heart wall
becomes stiffer during the ventricle blood filling. |
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16:36 |
712. |
Auto-Elastography of the Brain |
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Sha Zhao1,
Alan Jackson1, Geoffrey J. Parker1
1ISBE, University of Manchester, Manchester,
England, UK |
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We present our findings
of using a phase contrast imaging technique to
detect brain tissue’s motion induced by blood and
CSF pulsation. We present methods to enable the
calculation of elasticity from this motion, which
allows elastography with no external driving device.
We demonstrate that our measurements are compatible
with previous measurements of shear modulus in the
brain. |
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16:48 |
713. |
Anomalous Shear Wave
Propagation Reveals Micro-Architectural Properties -
Potential Implications for Diagnostic Imaging |
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Ralph Sinkus1,
Benoit Larrat1, Najat Salameh2,
Katja Siegmann3, Bernard Van Beers2,
Mathias Fink1
1Laboratoire Ondes et Acoustique, ESPCI,
Paris, France; 2Radiodiagnostic Unit,
Université Catholique de Louvain, Brussels, Belgium;
3Abteilung Radiologische Diagnostik,
Universitätsklinikum Tübingen, Tübingen, Germany |
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Anomalous shear wave
propagation reveals micro-architectural properties
of underlying hard scattering structures. This is
shown via simulations, phantom experiments,
in-vivo liver fibrosis and breast cancer data.
Thereby, unique information about the vascular
architecture of tumours at the clinical imaging
scale are accessible. |
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17:00 |
714. |
High Resolution
MR-Elastography Mouse Brain Study: Towards a
Mechanical Atlas |
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Elsa Diguet1,
Elijah van Houten2, Michael Green3,
Ralph Sinkus1
1Laboratoire Ondes et Acoustique, ESPCI,
Paris, France; 2University of Canterbury,
Christchurch, New Zealand; 3Prince of
Wales Medical Research Institute, Sydney, Australia |
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High resolution
MR-elastography is applied to image the mechanical
properties of mice brain in particular the corpus
callosum at 1000Hz. A reproducibility study shows
that the obtained values for the complex shear
modulus are stable (Gd:7%, Gl:25%) and that also
other myelinated structures are well visible like
the optic tract or the superior cerebellar peduncle. |
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17:12 |
715. |
A Protocol for Assessing
Hepatic Fibrosis in Iron-Overloaded Liver Tissue
with MR Elastography |
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David W. Stanley1,
Meng Yin2, Kevin J. Glaser2,
Richard L. Ehman2
1GE Healthcare, Proctor, MN, USA; 2Department
of Radiology, Mayo Clinic, Rochester, MN, USA |
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Patients that have had
high iron concentration in their liver tissue, which
leads to severely, shortened T2/T2*, can be
problematic at 3.0T because it produces poor MR
signal in the liver and MRE liver stiffness
measurements may not be valid due to the extremely
low SNR. We explored the relationship between the
SNR and the motion sensitivity of MRE by varying the
time duration of the motion-encoding gradients (MEG)
in the MRE pulse sequence. A modified MRE protocol
with broader receive bandwidth and fractional period
MEG was developed for use in patients with
iron-overloaded liver tissue. |
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17:24 |
716. |
TREMR: Table-Resonance
Elastography with MR |
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Daniel Gallichan1,
Matthew D. Robson2, Andreas J. Bartsch3,
Karla L. Miller1
1FMRIB Centre, University of Oxford, Oxford,
Oxon, UK; 2OCMR, University of Oxford;
3Neuroradiology, University of Würzburg |
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Low-frequency gradient
switching leads to substantial vibration of the
patient table. Here we successfully demonstrate that
these vibrations can be used to image the
propagation of vibrational shear waves through the
brain. This suggests a method allowing MR
Elastography to be performed without the need for
purpose-built hardware to generate the vibrations. |
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17:36 |
717. |
MR Acoustic Radiation Force
Imaging: In Vivo Comparison to Ultrasound
Motion Tracking |
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Yuexi Huang1,
Laura Curiel2, Aleksandra Kukic1,
Rajiv Chopra1, Kullervo Hynynen1,3
1Sunnybrook Health Sciences Centre, Toronto,
ON, Canada; 2Thunder Bay Regional
Research Institute, Thunder Bay, ON, Canada; 3Department
of Medical Biophysics, University of Toronto,
Toronto, ON, Canada |
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MR acoustic radiation
force imaging (MR-ARFI) was applied in vivo
on rabbit thigh muscle simultaneously with real-time
ultrasound motion tracking, by which time-resolved
displacement values during the MR measurement were
measured. Square-modulated focused ultrasound pulses
at 50 Hz were applied at 25W acoustical power with
1% duty cycle during the measurements. Time-averaged
results from the two modalities were compared.
Results showed general agreement between MR-ARFI and
the calculated ultrasound data. |
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17:48 |
718. |
Proper Orthogonal
Decomposition for Improved Assessment of Brain MR
Elastography: Initial Results |
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Curtis L. Johnson1,
Dimitrios C. Karampinos1,2, Danchin Chen1,
Bradley P. Sutton2,3, William C. Olivero2,4,
John G. Georgiadis1,2
1Mechanical Science and Engineering
Department, University of Illinois at
Urbana-Champaign, Urbana, IL, USA; 2Beckman
Institute for Advanced Science and Technology,
University of Illinois at Urbana-Champaign, Urbana,
IL, USA; 3Bioengineering Department,
University of Illinois at Urbana-Champaign, Urbana,
IL, USA; 4Department of Neurosurgery,
University of Illinois at Urbana-Champaign, Urbana,
IL, USA |
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The Proper Orthogonal
Decomposition (POD) method is proposed to extract
shear wave modes from human brain Magnetic Resonance
Elastography (MRE) data sets. The POD method allows
for mode extraction from a dynamic system regardless
of linearity. This is an improvement over current
MRE post-processing techniques which assume that the
harmonically actuated brain is a linear system,
possibly leading to variations in results between
studies. It is shown that POD can be used to extract
dynamic modes in the human brain during MRE
experiments, and can be used to improve data
analysis and create a simple, dynamic model of the
brain. |
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